Although the importance of many molecules expressed in atopic immune responses remains unclear, IL-4, IL-13 and molecules important for the function of these cytokines have been demonstrated to be essential for the development of allergic immune responses. Our interest has been in understanding the molecular mechanisms by which IL-4 signaling is regulated. Recently, a new family of proteins, termed Suppressors Of Cytokines Signaling (SOCS) has been identified. We have previously shown that SOCS-l is a potent inhibitor of JAK/STAT signaling activated by IL-4. SOCS-l expression is regulated both at the RNA and protein stability level. To identify proteins that bind, and potentially regulate, SOCS-1 we used the yeast two-hybrid system. We have identified the serine-threonine kinase Pim-2 as a binding partner for SOCS-1. Our preliminary studies demonstrate that SOCS-1 can interact with all three Pim kinases in mammalian cells. Co-expression of SOCS-l with Pim-2 leads to the expression of novel SOCS-l isoforms that represent phosphorylated forms of SOCS-1. In vitro studies demonstrate that Pim-2 can directly phosphorylate SOCS-1. Strikingly, coexpression of SOCS-l with Pim-2 increases the levels of SOCS-1 protein. Consistent with this result, expression of Pim-2 increases the inhibition of IL-4 signaling by SOCS-1. These data lead to a model by which the expression of the Pim-2 kinase alters SOCS-l function through a phosphorylation event that stabilizes the SOCS-1 protein. Our grant proposes experiments to test this model and to determine the role Pim kinases play in regulating SOCS-l function in vivo.